The phrase "almost mysterious" is correct and usable in written English.
It can be used to describe something that has an air of mystery but is not fully mysterious, often implying a sense of intrigue or curiosity.
Example: "The old mansion had an almost mysterious quality, with its darkened windows and overgrown garden."
Alternatives: "somewhat enigmatic" or "partially cryptic".
"We didn't want to do a literal masterpiece, but an almost mysterious single beam of modernity,'' said Shohei Shigematsu, the firm's senior associate on the project.
A trim, tightly knit man with curly dark-blond hair, blue eyes and a sharp, sun-weathered face, Stookey is self-contained, almost mysterious, genial yet watchful.
The stew, rich with the slight gaminess of lamb, the tang of sherry and the smooth comfort of white beans, was brought to greatness by the subtle heat and almost mysterious smokiness of the piment?
But what ultimately stays with many a visitor to the epicentre of Japan are the moments of stillness, of collectedness, of almost mysterious remoteness, where you see the changeless nerve centre from which all the wild changes arise.
It is almost mysterious, if I may say so myself, how even today when I go to the Uffizi Gallery and stand before true masterpieces like La Primavera or The Birth of Venus I feel, just like long ago, as if assailed by a kind of strange allure.
And while the mother-and-child reunion promised by the singer-songwriter Paul Simon often proves elusive even in real life, it doesn't require a spoiler alert to reveal that by the end of this film, three lives have been braided together in an unlikely and almost mysterious fashion.
Victoria noted the coincidence of the dates as "almost incredible and most mysterious".
The land of lie-flat beds and warm cookies may seem almost mystical or a bit mysterious to most travelers.
Ah, humanity!" is, in the story, almost as mysterious as Bartleby himself.
But sometimes I wondered if she was almost as mysterious to him as she was to me.
Out the window goes the dynamism of American self-invention; in comes something almost more mysterious: a reckoning with an apparently seamless life continuity.
